while messing around with the “fly” thing, i discovered an awesome time-waster (i needed more of those!): you go into fly mode and try and fly through a tunnel as fast as possible without touching the walls.
i set up a tube like this:
walked to the entrance:
and tried to do it as fast as possible! (shift-F to enter fly mode)
the only things you cant do are clip through the walls.
anyway, i find this great fun! 
